The long term objective of this proposal is the development if animal and in vitro models to elucidate the host-parasite interactions controlling the relationship between the nematode, Strongyloides stercoralis, and its hosts (man, primates and dogs). In these interactions the host usually prevails, resulting in a well-tolerated, self-limited infection. Sometimes neither host nor parasite prevails and a highly persistent, chronic infection is maintained. Occasionally the controls on parasite abundance and distribution fail, resulting in massive hyperinfection, sometimes with highly invasive, often fatal, disseminated infection.